In addition, the guys are beating with two primitive sticks, so they must be to the death.

In addition, the guys are beating each other with two primitive sticks, so they must be fighting to the death.

With some of the actions in English, it's important to explicitly state who or what is on the receiving end. Not only does it just sound weird and clumsy to say "They're beating." instead of "They're beating each other.", but it's also fairly common to say "He's beating it" to mean "He's masturbating." when you're talking about a boy or a man.
You should probably also note what it is that they're doing to the death. In this case, they're "fighting" to the death. It would be interesting to watch a cooking show where two chefs "bake" to the death, for example. Just like with the other correction, this makes the phrase sound more natural.

In English, when you give something a name, you "call it" that name or "call it by" that name. You don't "call it as" that name. If you're following it with the name itself you shouldn't use "by". If you're calling someone by their name but aren't saying the name, you should use "by".
If Mark, for example, was talking to Kara and used her first name, it could be said either "Mark called her 'Kara'." or "Mark called her by her first name.". In English, this isn't noteworthy, of course, but I think it'll give you a better perspective of what I'm talking about.

They aren't the oldest text editors in the world. But they are really old. So we can say that they would be on a list of the oldest text editors, or that they are two of the oldest text editors. Emacs came out in 1976, and Vim came out in 1991, but O26 came out in 1967.
It would be more correct to describe them as "the oldest surviving text editors" as text editors like O26 are almost never used today in the same way emacs and vim are. In other words, O26 has died, but emacs and vim still survive.

The central character is Nancy who begins selling marijuana to support her family after her husband dies because of his sudden heart attack.

The main character is Nancy, who begins selling marijuana to support her family after her husband dies due to a sudden heart attack.

Central character is actually correct, but usually, when talking about works of literature, in English, we say "main character" instead. This is just me being picky.
The thought, "The main character is Nancy." could be its own full thought with a meaning of its own. The phrase "who begins selling marijuana ... sudden heart attack" is not a complete thought. Whenever we join a complete thought, which is called an "independent clause", with an incomplete thought, which is called a "dependent clause", in English, we have to separate them out with commas.
Once again, I'm just being picky. When we're talking about causes of death, this is how we'll usually say it.

Also, I think that the comic artist must be a Buddhist, so the fiction must have been affected by the teaching.

Also, I think that the comic artist must be a Buddhist, so the story must have been influenced by the Buddhist teachings.

In America we don't call stories fiction. We use fiction when we are referring to the genre.
It was a work of fiction.
I like reading fiction more than nonfiction.
Affect and influence mean the same thing, but influence is used in more about the mental changes, or changes to thoughts, and affect is more about physical changes.
Driving while influenced by alcohol will affect your ability to drive.
The alcohol influenced your mind, and affected your physical ability to drive well.
I added Buddhist to make it more clear what teachings were being talked about.

One of my friends who got to know at a language exchange event invited me to join it.

One of my friends, who I got to know at a language exchange event, invited me to join it.

The phrase "who I got to know at a language exchange event" helps clarify which friend you are talking about, but is not essential to the sentence, so it is offset by commas. This is called a nonessential clause.

とんでもないです。ところで、この条件はing の形だけではない。 他の例え： I like reading, to dance, and the art of singing. X 違う I like reading, dancing, and singing. I like to read, dance, and sing. I like the quietness of reading, the flair of dancing, and the art of ...